1. Field of the Invention
This invention generally relates to a leak diagnostic device for a fuel vapor processing device of an internal combustion engine. More specifically, the present invention relates to a leak diagnostic device for an in-tank canister system.
2. Background Information
A fuel vapor processing device is a device for preventing fuel vapor inside a fuel tank from being dispersed into surrounding atmosphere. There have been fuel vapor processing devices for internal combustion engines, in which fuel vapor vaporized in a fuel tank is guided to and is temporally absorbed in a canister. Inside the canister, activated carbon absorbs the fuel vapor, such that the fuel vapor is not discharged to the atmosphere. The fuel vapor absorbed in the canister is thereafter purged out of the canister into a suction system of the internal combustion engine via a purge control valve, as air flows in from an air inlet opening. In this manner, dispersion of the fuel vapor from the fuel tank into the surrounding atmosphere can be avoided.
However, if such vapor processing device has a hole, crack or seal failure in its fuel tank, canister and/or the conducting pipes, it causes a leakage of the fuel vapor. In other words, the vapor processing device cannot properly prevent the dispersion of the fuel vapor into the surrounding atmosphere.
To address such problem, a diagnostic system that diagnoses a leakage by using negative pressure measurements has been proposed as a leak diagnostic device for diagnosing leaks in a purge line, as well as a fuel tank and a canister. (Japanese Unexamined Patent Publication No. 5-195881)
In this system, a leak diagnosis is performed at a predetermined timing during operation of the internal combustion engine. As the leak diagnosis starts, the air inlet passage that leads to the canister is closed at a cutoff valve or drain cut valve, while keeping the purge control valve open. As a result, the fuel vapor and air inside the canister are purged out of the canister to the suction system of the internal combustion engine, but air does not flow in from the air inlet passage. Therefore, negative pressure is effected in the fuel tank and the canister, as well as in the purge line that connects the canister and the suction system. Then, the purge control valve, which is located between the canister and the suction system, is closed. Thereafter, a change in the negative pressure within the fuel tank is continuously measured by a pressure sensor. After a predetermined period of time elapses, the leak diagnostic system determines whether there is a leak, based on the measurement of the negative pressure. That is, if the negative pressure within the fuel tank remains the same, there is no leak in the purge line, the fuel tank, or the canister. If, on the other hand, the negative pressure within the fuel tank has decreased and become closer to the atmospheric pressure, there is a leak. Even if the leak takes place in the canister, the leak affects the pressure in the purge line and the fuel tank. Therefore, once a leak is detected, the leak can be in any of the purge line, the fuel tank, and the canister. This determination is made with reference to a predetermined threshold level pressure. If the negative pressure of the fuel tank is equal to or greater than the threshold level after the predetermined period of time, there is no leak. Conversely, if the pressure is smaller than the threshold level and is approaching the atmospheric pressure, there is a leak somewhere in the purge line, fuel tank, and the canister.
In recent years, there has been proposed a fuel vapor processing device of an internal combustion engine for use in an in-tank canister system, as seen in Japanese Unexamined Patent Publication No. 10-184476. The in-tank canister system has a canister within a fuel tank. This system is preferable in that it can dispose most of the conducting pipes within the fuel tank. Therefore, dispersion of fuel vapor from rubber hoses and joints that connect the fuel tank and the canister does not necessarily result in dispersion of fuel vapor out of the fuel tank.
In order to apply the aforesaid leak diagnosis that uses negative pressure measurements in an in-tank canister system, a cutoff valve or drain cut valve that controls the flow of air must be disposed in the air inlet passage between the canister and the air inlet opening. In the case of the in-tank canister system, the canister is inside the fuel tank, while the air inlet opening is outside the fuel tank. The cutoff valve should be disposed outside the fuel tank, since the cutoff valve is generally formed of a solenoid valve, and it is not desirable to dispose an electrical component such as a solenoid valve in the fuel tank.
To perform the leak diagnosis in this type of in-tank canister system, first the cutoff valve is closed, while the purge valve is kept open to create negative pressure within the fuel tank and the canister. Then, the purge control valve is closed to perform the leak diagnosis. However in this leak diagnosis, if there is a hole in the canister, the hole will not be detected. This is because the pressure within both the fuel tank and the canister is negative. Since the pressure inside the fuel tank is the same as the pressure inside the canister, the pressure inside the fuel tank will not be affected even if there is a hole in the canister.
In another type of in-tank canister system, a check valve or negative pressure cut valve is disposed in a fuel vapor inlet passage that guides the fuel vapor to the canister from the fuel vapor inlet opening. The fuel vapor opening opens to the upper interior space of the fuel tank. In this type of in-tank canister system, a bypass passage is disposed so as to bypass the negative pressure cut valve. Also, a bypass valve is disposed in the bypass passage such that the bypass valve opens only during the leak diagnosis to create negative pressure within the fuel tank. Therefore, to perform leak diagnosis in this type of in-tank canister system, both the cutoff valve and the bypass valve must be provided, which leads to an undesired increase in the number of the components required.
In view of the above, there exists a need for a leak diagnostic device which overcomes the above mentioned problems in the prior art. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.
Accordingly, an object of the present invention is to provide a leak diagnostic device that can detect leaks at any parts of the in-tank canister system that is related to a release of the fuel vapor.
Another object of the present invention is to provide a leak diagnostic device that requires a fewer number of parts.
Still another object of the present invention is to provide a leak diagnostic device that can detect a leak as well as a leakage point in an in-tank canister system.
The foregoing objects can basically be attained by providing a leak diagnostic device for an in-tank canister system connected to a suction system of an internal combustion engine. The in-tank canister system includes a fuel tank, fuel tank, a vapor absorbing canister, a fuel vapor inlet passage, an air inlet passage, and a purge passage. The fuel vapor inlet passage fluidly connects a fuel vapor inlet opening disposed in an upper interior space of the fuel tank to the canister via a negative pressure cut valve. The air inlet passage draws air into the canister through an air inlet opening disposed outside the fuel tank. The purge passage purges the fuel vapor along with air out of the canister into the suction system of the internal combustion engine via a purge control valve. The leak diagnostic device comprises a negative pressure control valve and a control unit. The negative pressure control valve is arranged to operatively connect and disconnect the suction system between the canister in a normal mode and the upper interior space of the fuel tank in a diagnosis mode. The control unit has a pressure sensor arranged to measure pressure in the upper interior space of the fuel tank. The control unit is operatively coupled to the negative pressure control valve to shift the negative pressure control valve between the normal mode and the diagnosis mode. The control unit is configured to open the purge control valve with said negative pressure control valve in said normal mode to create a negative pressure in the fuel tank and to determine whether there is a leak based on the pressure measured by said pressure sensor.
These and other objects, features, aspects and advantages of the present invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. The features of the present invention that are believed to be novel are set forth with particularity in the appended claims.